This is what happened to Tuukka Rask Thursday night. The Bruins were on their way to a Game 4 clinching win against the Rangers. They were going to get up to a week off before the Eastern Conference finals.

And then Tuukka fell. Butt over tea kettle. His skate hit a rut in the crease and he tumbled backward and Carl Hagelin’s weak backhander bounced and bounced and bounced and finally . . . trickled over the goal line while Tuukka tried to recover from his fall.

And that was the beginning of the . . .

Worst . . .

Loss . . .

Ever.

OK, we exaggerate. Thursday’s 4-3 Rangers’ overtime victory no doubt merely postpones a Boston series victory. The Bruins still lead it, 3-1, and should wrap things up Saturday at TD Garden.

But they will be reminded that three years ago — with Tuukka between the pipes — they blew a 3-0 series lead against the Flyers. They will be reminded that they seem to have a big problem closing out playoff series. They will be reminded that they gave away Game 4 in Madison Square Garden. Big time.

“I lost my balance and the rest is history,’’ said Rask, a stand-up guy in the losers’ locker room.

He had company in the goat house. Zdeno Chara, a Boston leader/captain on par with John Havlicek or Tom Brady, coughed up the puck in lazy fashion (perhaps he’s tired from playing a million minutes every night), which led to New York’s second goal. And coach Claude Julien, officially the winningest coach in Bruins playoff history, got hung with a too-many-men-on-the-ice penalty that led to the third Rangers goal.

The winning goal, the overtime strike by Chris Kreider that came in the eighth minute of overtime, was the Rangers’ most legit of the night.

The first two were softer than the belly of an Ipswich clam. And they gave life to the moribund Rangers.

The Bruins outshot the Rangers, 12-4, in the first period and the Rangers were 2 for 40 on the power play in the playoffs in the middle of the second when Tuukka fell.

He fell as Hagelin (the guy who Rangers coach John Tortorella said “stinks” on the power play) broke across the blue line and took a pass from Derick Brassard.

“I just took a step to the side in what I think was a skate mark or something,’’ said Rask. “My skate dug in, that’s what it felt like. It happens to me twice a year in practice, maybe. Focus, got to be more focused, I think. Just a tough mistake. It looks pretty bad on TV, I guess.’’

Rask toppled backward as Hagelin approached. With Johnny Boychuk contesting, Hagelin was barely able to get any wood on his backhand. He managed a little Mookie Wilson dribbler that trickled across the goalmouth while Rask floundered like a beached seal.

You could almost hear Vin Scully saying, “Behind the bag! And the Mets win!’’

The fluke goal gave the Rangers hope. And then the Bruins gave them another present. After Rask stopped a shot and casually slipped the puck to Chara, Big Z got his pocket picked by Derek Stepan. Stepan’s stunning wraparound made it 2-2.

“We gave ’em a couple of gifts,’’ acknowledged Rask.

After the Bruins regained the lead on Tyler Seguin’s first goal of the playoffs, we saw the ghost of Grapes and too many men on the ice. That’s when Artie Boyle’s son Brian tied it on a power-play goal from out front.

“A breakdown in front of our net,’’ explained Rask.

You knew it was going to be bad after that. The Bruins had given the Rangers too many chances.

The first goal, the one when Tuukka fell, will lead all the lowlight reels.

Henrik Lundqvist, New York’s all-planet goalie, said, “Probably the ugliest goal I have ever seen turned it around for us, and that’s hockey. A save or a goal or one shift can change everything. Tonight it was an ugly goal. Sometimes that’s all you need to get us going, to get the building going.’’

“Stupid mistakes cost us the game,’’ said Rask. “It’s a game of mistakes. We’ve just got to learn from them and move forward. Shake it off and move on.’’

They’d better win Saturday. Or they’ll have to come back to New York and there will be thousand more reminders that Rask was between the pipes in 2010 when the Bruins blew a 3-0 lead against the Flyers.